1. Field of the Invention
The present invention relates to a sheet conveying apparatus capable of correcting a skew of a sheet and an image forming apparatus having the sheet conveying apparatus.
2. Description of the Related Art
In conventional image forming apparatuses for forming an image on a sheet, in order to form the image without a skew onto the sheet, a sheet conveying apparatus capable of correcting the skew of the sheet conveyed to an image forming unit is provided.
The configurations discussed in Japanese Patent Application Laid-Open No. 6-336353 and Japanese Patent Application Laid-Open No. 9-183539, a skew of a sheet is corrected by bringing the leading edge of the sheet into contact with a contact portion such as a nip portion of a registration roller pair and a shutter so as to form a loop of the sheet and to make the leading edge of the sheet fit along the nip portion.
In recent image forming apparatuses, there has been growing demands for forming an image onto various types of sheets of different sizes, different grammage, and different surface glossiness with enhanced productivity with a more compact body. Unfortunately, the conventional sheet conveying apparatuses have been in need of some improvements in achieving the high productivity while maintaining the skew correction performance for the various types of sheets.
For example, in conveying a sheet of a large grammage (so-called thick paper), since the sheet stiffness is large, the sheet slips at the nip portion of the roller pair provided upstream of the above-described contact portion when correcting the skew of the sheet. This may cause failure in the formation of the sheet loop of a desired size required to correct the skew of the sheet. If the sheet loop of the desired size cannot be formed, the skew of the sheet cannot be corrected. As a result, the image cannot be formed at an appropriate position on the sheet, causing an image failure. In consideration of the slip, if the loop formation is continued until the loop of a predetermined size is formed, the productivity may be significantly decreased. In other words, for the thick paper, the conventional sheet conveying apparatuses have not been able to achieve sufficient skew correction performance while maintaining high productivity.